linux-kernel - Re: [PATCH 11/20] sound, skylake: switch from ioremap

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Message-ID: <CAPcyv4jper5Byz2782MHbi-_RjDiDna4hYCHG1UBacE3YXd96A@mail.gmail.com>
Date:	Mon, 19 Oct 2015 09:59:29 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Takashi Iwai <tiwai@...e.de>, Liam Girdwood <lgirdwood@...il.com>,
	Jeeja KP <jeeja.kp@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Jaroslav Kysela <perex@...ex.cz>, linux-arch@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/20] sound, skylake: switch from ioremap_cache to memremap

On Mon, Oct 19, 2015 at 9:08 AM, Mark Brown <broonie@...nel.org> wrote:
> On Mon, Oct 19, 2015 at 05:34:48PM +0200, Takashi Iwai wrote:
>> Mark Brown wrote:
>
>> > On Fri, Oct 09, 2015 at 06:16:36PM -0400, Dan Williams wrote:
>> > > In preparation for deprecating ioremap_cache() convert its usage in
>> > > skl-nhlt to memremap.
>
>> > > -void __iomem *skl_nhlt_init(struct device *dev)
>> > > +void *skl_nhlt_init(struct device *dev)
>
>> > Why are we loosing the annotation here?
>
>> It's the exact purpose of this patchset, as far as I understand.
>> memremap() allows the driver accessing the mapped memory just like a
>> normal memory unlike ioremap().
>
> There's no mention of what the purpose of the conversion is in either
> the patch or the cover letter so it's a bit unclear, some confirmation
> would be good :(

The cover letter linked this article which talked through the
motivation: https://lwn.net/Articles/653585/

Essentially an "__iomem" annotation on a cached mapping is
inconsistent as __iomem indicates "may have side effects, use special
accessors" and cached means "pre-fetching, asynchronous write-backs,
and cpu determined i/o sizes are permissible".
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